This 8051 microcontroller based digital voltmeter is used to measure up to 5 volts. This project is designed using AT89S51 microcontroller and ADC0804 is nothing but ADC (Analog to Digital Conversion). The output is displayed by using two seven segment displays. The software of this voltmeter is developed in assembly language. Before choosing this digital voltmeter project one should know the concepts of interfacing 7-segment display to the 8051 microcontroller and interfacing ADC to 8051 microcontroller. Because, these topics will give you a basic idea.